Baseplate for an electronic module and method of manufacturing the same

ABSTRACT

Various embodiments provide methods for manufacturing a baseplate for an electronic module and an electronic module comprising a baseplate, wherein the baseplate comprises a conductive material; and a recess formed in one main surface of the baseplate and being adapted to accommodate an electronic chip.

RELATED APPLICATION

This application is a divisional of application Ser. No. 14/251,609,filed on Apr. 13, 2014 and published on Oct. 15, 2015 as US2015/0294931, now pending. The patent application identified above isincorporated herein by reference in its entirety to provide continuityof disclosure.

TECHNICAL FIELD

Various embodiments relate to a baseplate for an electronic module, anelectronic module and method of manufacturing a baseplate for anelectronic module.

BACKGROUND

In many technical fields electronic modules, e.g. so called powermodules, are used for providing or switching power to electricalcomponents or devices. One possible field is the automotive field, forexample. Most of the power modules comprises at least one transistor,e.g. an IGBT (insulated gate bipolar transistor). Efficiency within anIGBT power module is a major challenge when designing new power modules.One factor that affects the efficiency and possible switchingfrequencies of a power module is stray inductance. Stray inductance isdirectly influenced by the design of the power module and less by thebasic physics of the module. Conventional IGBT power module designs tendto sacrifice stray inductance in order to increase power density of themodule. This normally includes separating the positive (+) and negative(−) DC paths on the substrate, laterally bonding across the main currentflow path to ease the bonding of the power transistor chips to variouspotentials in the power module, and/or providing repetitive layouts forthe ease of manufacture due to the number of common elements present inthe module. In each case, the result is an increase in stray inductancewithin the power module and thus reduced efficiency. Furthermore,standard power modules using bare dice are presently used also in thelower power ranged and having the drawback of high costs, especially forsmall volumes.

SUMMARY

Various embodiments provide a baseplate for an electronic module,wherein the baseplate comprises a conductive material; and a recessformed in one main surface of the baseplate and being adapted toaccommodate an electronic chip.

Furthermore, various embodiments provide an electronic module,comprising a baseplate according to an exemplary embodiment and anelectronic chip placed in the recess of the baseplate.

Moreover, various embodiments provide a method of manufacturing abaseplate for an electronic module, wherein the method comprisesproviding a baseplate; and forming a recess in one main surface of thebaseplate, wherein the recess is adapted to accommodate an electronicchip.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. The drawings are not necessarilyto scale. Instead emphasis is generally being placed upon illustratingthe principles of the invention. In the following description, variousembodiments are described with reference to the following drawings, inwhich:

FIG. 1 shows a perspective view of components of an electronic module;

FIG. 2 shows a perspective view of the electronic module of FIG. 1including an insulating layer; and

FIG. 3 shows a side view of the electronic module of FIG. 2.

DETAILED DESCRIPTION

In the following further exemplary embodiments of a semiconductor deviceand a method of manufacturing a semiconductor device will be explained.It should be noted that the description of specific features describedin the context of one specific exemplary embodiment may be combined withothers exemplary embodiments as well.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration”. Any embodiment or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs.

Various embodiments provide a method of manufacturing an electronicmodule, wherein the method comprises providing a baseplate according toan exemplary embodiment; arranging an electronic chip in the recess ofthe baseplate. Preferably, the electronic chip is electrically and/orthermally contacted to the baseplate either directly or indirectly. Forexample, the electronic chip may be adhered to a contacting area in therecess, e.g. by using an (conductive) epoxy adhesive or solder.Optionally, a cover or insulating layer may be arranged on the one mainsurface of the baseplate and covering the arranged electronic chip. Inaddition or alternatively a mold compound may be formed around at leastportions of the baseplate and may form an encapsulation of theelectronic module.

In particular, the electronic module may be a power module. For example,the electronic chip may be a die, a packaged electronic chip orpre-packaged die. The recess of the baseplate may form a blind hole.Preferably, the recess may have a depth corresponding or adapted to athickness of the electronic chip intended to be placed or arranged inthe recess. Preferably, the electronic chip is a packaged electronicchip, e.g. may comprise a molded encapsulation. For example, theelectronic chip may be a small outline transistor (SOT) package or smalloutline nonleaded transistor (SON) package. In particular, the carriermay comprise a plurality of recesses. While lateral sizes of thebaseplate and the electronic module may be adapted with respect to anydesired application of the same, typical sizes of the baseplate may bein the range of 10 mm to 200 mm in both lateral dimensions.

By providing a recess in a baseplate for an electronic module it may bepossible to produce application specific low cost power sub-systemsusing SOT and/or SON packages which may be arranged in the recess. Thismay enable cheaper solutions than standard power modules in the powerrange from few hundred watts up to 10 kW or even more. Furthermore, theconductive material of the baseplate, which partially surround theelectronic chip, may allow to significantly reduce stray inductances ofthe power package which in turn may allow fast switching devices (IGBT,diodes and/or MOSFETs) to be used reducing significantly power losses. Apotential application may be a power module for a welding machine, forexample.

In the following exemplary embodiments of the baseplate are described.However, the features and elements described with respect to theseembodiments can be combined with exemplary embodiments of the electronicmodule and the method of manufacturing a baseplate as well.

According to an exemplary embodiment of the baseplate the recess has adepth adapted to fully accommodate the electronic chip.

In particular, the depth of the recess may be in range between 1 mm and10 mm, preferably in the range between 2 mm and 7 mm, more preferably inthe range between 2.5 mm and 5.5 mm. It should be noted that preferablythe recess may have a depth which is suitable that the electronic chipcan be accommodated together with a substrate or carrier the electronicchip or die is attached to.

According to an exemplary embodiment of the baseplate the baseplate hasa thickness in the range between 2.5 mm and 7 mm.

In particular, the thickness of the baseplate may be in the rangebetween 3.0 mm and 6.0 mm, preferably between 3.5 mm and 5 mm. The useof relative low baseplates comprising a recess into which the electronicchip, e.g. a pre-packaged dice, may be arranged may ensure highperformances at high switching frequency due to the reduced height andtotal parasitic parameters due to the conductive material of thebaseplate and due to potential very low coupling capacitances.

According to an exemplary embodiment of the baseplate the baseplatecomprises a material selected out of the group consisting of aluminum,brass and copper.

In principle, any suitable metal or other material which is commonlyused for baseplates or carriers may be used. The base plate may compriseone or several of the materials or may consist of one or several ofthese materials. Said baseplate might comprise Metal Matrix Composite orother sintered metals. In particular, the material should have a thermaland/or electrical conductivity suitable for the intended application.For example it may be possible to provide a relatively cost efficientaluminum based baseplate.

According to an exemplary embodiment of the baseplate in the recess acontact area is formed.

In particular, the contact area or a plurality of contact areas may formcontact pads, pins or contact terminals adapted to be electricallycontacted to terminals or pads of the electronic chip or chip package.For example, the contact areas may be adapted for surface mountingtechnology, i.e. may be adapted that a surface mounting device iscontacted to the contact areas. In addition or alternatively, thecontact areas or the baseplate itself may also function as heatsinks.Additionally, it should be mentioned that the electronic chip, includinga potential substrate it is mounted on, can be attached to the contactarea by an adhesive: like an epoxy adhesive, a solder or sintered layer.

In the following exemplary embodiments of the electronic module aredescribed. However, the features and elements described with respect tothese embodiments can be combined with exemplary embodiments of thebaseplate and the method of manufacturing a baseplate as well.

According to exemplary embodiments of the electronic module theelectronic chip is a pre-packaged dice.

The using of a potential low cost leadless or leaded pre-packaged dicemay enable different pick-and-place methods and low cost manufacturingprocesses. In case pre-packaged dices are used also the sensitivity ofthe electronic module or device to production issues and may lead tohigher reliability of the electronic module itself due to mechanical andchemical protection offered by SOT and SON packages. In addition thismay strongly reduce the needs to creepage distance towards packagingplastic cover and may reduce the total height of the electronic moduleor power module. It may also be possible to apply a mechanical pressuredirectly on top of the electronic chip or pre-packaged dice once it hasbeen arranged or assembled in the recess of the baseplate. Thus, it maybe possible to improve the thermal resistance due to providing a betteradhesion to the baseplate or heatsink. This technology as well mayenable double sided cooling solutions.

Furthermore, the use of pre-packaged dices may enable a betterinsulation of the electronic chips which is sometimes demanded bymanufacturers or users in order to avoid the possibility that a user oroperator can come in contact with swinging portions of the electronic orpower module, like heatsinks which may swing at high voltages, forexample. In addition the double isolation and in particular the use ofan electrical conductive material for the baseplate, forming a portionof a second isolation (in particular with respect to stray fields) theelectronic module may have a relative low stray inductance even if thepackage (e.g. SON or SOT) may have a relative high stray inductance.

In addition, the use of pre-packaged dice may enable high reliability ofthe electronic module, especially in high temperature and high humiditystress, like conditions described in the HTRB, HTGS, AC, THB, and H3TRBtests.

According to exemplary embodiments of the electronic module theelectronic chip is attached to the baseplate.

For example, the electronic chip may be attached by surface mountingtechnology directly or indirectly to the baseplate. For example, theelectronic chip or die may be attached to a substrate or carrier bysurface mounting technology, while the substrate or carrier is attachedto the baseplate by an adhesive, for example. Preferably, the electronicchip is attached to the baseplate in such a way that the electronic chipis completely accommodated by the recess. That is, the thickness of theelectronic chip including an optional attachment or adhering layer ispreferably smaller than a depth of the recess. For example, when usingpre-packaged SON and/or SOT (forming isolated sub-assemblies) attachedor mounted onto PCB substrate or even directly on the baseplate in therecess the baseplate may as well form a heatsink. Thus, it may bepossible to avoid a split heatsink and a complex mechanical structure tosustain a split or separated heatsink which may in turn significantlyreduce the costs in the manufacturing process.

According to an exemplary embodiment of the electronic module theelectronic chip is arranged on a carrier.

The carrier or substrate may then be attached to the baseplate. Inparticular, the carrier may be a substrate, a direct bonded copper (DBC)substrate or carrier.

According to an exemplary embodiment of the electronic module theelectronic chip is adhered to the baseplate.

For example an epoxy adhesive or solder may be used for adhering theelectronic chip to the baseplate, in particular in the recess of thebaseplate. As already mentioned this may be done either directly orindirectly.

According to an exemplary embodiment the electronic module furthercomprises an insulating layer arranged on the one main surface of thebaseplate.

For example, the insulating layer may comprise or may be formed orconsist of a thin foil or film of a suitable insulating material likeKapton. By providing such an insulating or cover layer it may bepossible to arrange, e.g. by soldering, a PCB on top of the electronicmodule. Alternatively or additionally, a conductive layer may bearranged on the one main surface. It should be mentioned that the thinfoil or film may have a size or cover an area which is larger than anarea or size of the baseplate. That is, the thin foil or film may extendfurther than the baseplate. Alternatively, the size of the thin foil orfilm may be smaller or equal to the size or area of the base plate. Forexample the thin foil or film may exactly cover the base plate.

According to an exemplary embodiment the electronic module furthercomprises a mold compound at least partially encapsulating the baseplateand the electronic chip placed in the recess of the baseplate.

According to an exemplary embodiment the electronic module furthercomprises terminals arranged to contact the electronic chip with anexterior of the electronic module.

In particular, the terminals may be any suitable terminals, like snap-interminals, pressfit terminals, spring terminal, or any otherinterlocking terminal having a mechanical and an electricalfunctionality at the same time.

According to an exemplary embodiment the electronic module comprises aplurality of baseplates and a plurality of electronic chips placed inthe plurality of recesses of the plurality of baseplates.

In particular, in each recess of each baseplate the same number ofelectronic chips (optionally arranged on substrates or carriers) may bearranged or placed, e.g. in each recess one, two, three, or even moreelectronic chips may be placed. However, the number of electronic chipsper recess and/or per baseplate may be different.

According to exemplary embodiments of the electronic module at least twoof the plurality of baseplates are stacked on top of each other.

Thus, a stack of electronic chips or modules may be formed, wherein eachbaseplate preferably comprises at least one electronic chip attached inthe recess of the baseplate. By stacking the plurality of electronicchips on top of each other it may be possible to provide a space savingelectronic module. Furthermore, by stacking a plurality of electronicchips on top of each other the baseplate of one stack layer or level mayform a cover layer for the stack layer or level arranged below in thestack.

According to exemplary embodiments the method of manufacturing abaseplate the recess is formed by one process out of the groupconsisting of drilling; etching; punching; stamping; machining; milling;3D-printing; extruding and/or cold-extruding.

In particular, the drilling or etching may be performed by laser, aselective or non-selective etching agent, or the like.

In the following an exemplary embodiment of an electronic moduleincluding a baseplate according to an exemplary embodiment is describedin connection with the figures.

In particular, FIG. 1 schematically depicts a perspective view of acomponents of an electronic module 100 comprising a baseplate 101 inwhich a recess or cavity 102 is formed. The baseplate 101 comprises orconsists of a (thermally and electrically) conductive material likecopper, copper alloy, aluminum or aluminum alloy or any other suitablematerial. In addition to the recess 102 the baseplate 101 may compriseadditional structures or pattern like through holes 103 and/or lateralchannel or notches 104 for fixing. It should be mentioned that accordingto the embodiment of FIG. 1 the recess 102 is formed by a blind hole andnot by a through hole. Onto the bottom of the recess a substrate orcarrier 105 like a direct copper bond (DCB) package is fixed. Forexample, the substrate 105 may be glued or soldered to the bottom of therecess 102.

Before the substrate 105 is fixed to the baseplate 101 electronic chips106 like pre-assembled SOT or SON, VSON (IGBT/MOS) are assembled to thesubstrate, e.g. DBC. For the assembly of the electronic chips onto thesubstrate standard SMD pick and place machines can be used. In additionto the electronic chips standard and potential low cost terminals 107are soldered to the substrate. It should be mentioned that the recess orcavity is deep enough to accommodate the substrate having mountedthereon the electronic chips 106. The cavity or recess 102 may avoid thenecessity of a special plastic housing, as the baseplate forms the mainparts of a housing or enclosure. Thus, it may as well be possible toreduce the cost by avoiding the use of a special plastic housing butusing relative cheap material like aluminum of the baseplate as thehousing. In addition to the gluing of the substrate silicone rubber(like SilGel), epoxy or other materials may be used as additionalinsulator. The electronic module may thus, due to the materials and theused process techniques (like SMD pick and place techniques) form or bepart of a low cost power hybrid subsystem.

FIG. 2 schematically shows the embodiment of FIG. 1 having arrangedthereon a thin layer 210 or foil of an insulator material, like Kaptonwhich forms a part of the insulation of the substrate arranged(soldered, glued) in the recess of the baseplate. In order to use theterminals 107 for electrically contacting the electronic chips theterminals 107 projects out of the thin layer 210. This insulation layer210 may ensure creepage and clearance distances once the electronicmodule is assembled on boards, e.g. onto a PCB or once a PCB board issoldered on top of the electronic module. The thin layer 210 may alsoextend beyond the baseplate or a body of the electronic module so thatit may be avoidable that the baseplate, forming a heatsink is facingdirectly with the board fixed or soldered thereon.

FIG. 3 schematically shows a side or lateral view of the electronicmodule of FIG. 2. In particular, FIG. 3 shows sidewalls of the baseplate101 and the terminals 107 extending over the top of the electronicmodule 100 in order to enable an electrically contacting of theelectronic chips in the recess of the baseplate. The electronic module100 may form an extremely thin subsystem and providing specificcompensation paths so that it may be applied or used in systemsoperating at high switching frequency and in application requiringreduced vertical dimensions.

It should be noted that the term “comprising” does not exclude otherelements or features and the “a” or “an” does not exclude a plurality.Also elements described in association with different embodiments may becombined. It should also be noted that reference signs shall not beconstrued as limiting the scope of the claims. While the invention hasbeen particularly shown and described with reference to specificembodiments, it should be understood by those skilled in the art thatvarious changes in form and detail may be made therein without departingfrom the spirit and scope of the invention as defined by the appendedclaims. The scope of the invention is thus indicated by the appendedclaims and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced.

What is claimed is:
 1. A method of manufacturing a baseplate for anelectronic module, the method comprising: providing a baseplate; forminga recess in one main surface of the baseplate, wherein the recess isadapted to accommodate an electronic chip.
 2. The method according toclaim 1, wherein the recess is formed by one process out of the groupconsisting of: drilling; machining; milling; etching; punching;stamping; extruding; cold extruding; and 3D-printing.
 3. The methodaccording to claim 1 wherein the baseplate comprises a conductivematerial.
 4. The method according to claim 1, wherein the electronicmodule is a power module and the baseplate consists of electricallyconductive material.
 5. The method according to claim 1, wherein formingthe recess comprises forming the recess with a depth adapted to fullyaccommodate the electronic chip.
 6. The method according to claim 1,wherein the baseplate has a thickness in the range between 2 mm and 10mm.
 7. The method according to claim 3, wherein the baseplate comprisesa material selected out of the group consisting of: aluminum; brass;copper; and Metal Matrix Composite.
 8. The method according to claim 1,further comprising: forming a contact area in the recess.
 9. A method ofmanufacturing an electronic module, the method comprising: manufacturinga baseplate according to claim 1, and placing an electronic chip in therecess.
 10. The method according to claim 9, wherein the electronic chipis a pre-packaged dice.
 11. The method according to claim 9, furthercomprising attaching the electronic chip to the baseplate.
 12. Themethod according to claim 11, further comprising adhering the electronicchip to the baseplate.
 13. The method according to claim 9, furthercomprising providing an insulating layer arranged on the one mainsurface of the baseplate.
 14. The method according to claim 9, furthercomprising attaching the electronic chip to a substrate or carrierbefore placing the electronic chip in the recess.
 15. The methodaccording to claim 9, further comprising providing a mold compound atleast partially encapsulating the baseplate and the electronic chipplaced in the recess of the baseplate.
 16. The method according to claim9, further comprising providing terminals arranged to contact theelectronic chip with an exterior of the electronic module.
 17. Themethod according to claim 9, comprising manufacturing a plurality ofbaseplates according to claim 1 and placing a plurality of electronicchips in the plurality of recesses of the plurality of baseplates. 18.The method according to claim 17, further comprising stacking at leasttwo of the plurality of baseplates on top of each other.
 19. The methodaccording to claim 9, wherein the electronic module is a power moduleand the baseplate consists of electrically conductive material.
 20. Amethod of manufacturing an electronic power module, the methodcomprising: providing a baseplate consisting of an electricallyconductive material; forming a recess in one main surface of thebaseplate; and placing an electronic chip in the recess.